The preparation of a corrective lens for eyeglasses comprises firstly optically designing and then producing the refractive faces of the lens, and secondly adapting the lens to the selected frame. The present invention relates to measuring geometrico-physiognomic parameters on the wearer's face to provide information about the configuration in which the eyeglasses are to be placed on the wearer's face. These parameters can then be used in both of the stages in preparing a corrective lens so as to ensure that the lens ends up performing the corrective optical function for which it was designed and prescribed. In practice, the parameters concerned are mainly the following, considered when the wearer is in an orthostatic posture looking at the horizon at infinity:                the pupillary half-distances, i.e. the horizontal distances between the pupils and the sagittal plane;        the pupil heights, i.e. the substantially vertical distances between the projections of the pupils along the primary gaze axis (at infinity) onto the lens, either relative to the bottom edge of the frame or of the shaped lens (so-called “datum” definition), or else relative to the tangent to said edge at its lowest point (so-called “boxing” definition);        the distance between each lens and the corresponding eye; and        the pantoscopic angle of inclination formed by the general plane of the frame or of the lens relative to the vertical.        
In order to be taken effectively into account, these parameters need to be measured with care and accuracy, and that can be difficult in practice. In order to rationalize the taking of such measurements, proposals have been made to take the measurements from digital photographs of the wearer's face wearing the frame. Thus, by way of example, the pupillary half-distances and the pupil heights are measured by processing a digital image of the wearer's face taken in front view. In order to obtain the desired measurement accuracy, it has in the past been considered as essential for the image-capture appliance to be mounted to move vertically on a column of a stand that ensures that the optical axis of the lens of the image-capture appliance remains horizontal and can be adjusted to the appropriate height. That is intended to avoid vertical parallax errors that would otherwise run the risk of being made, in particular when measuring eye heights.
Nevertheless, the resulting measurement-taking device turns out to be relatively bulky and not very ergonomic for use on sales' premises. Furthermore, the measurement-taking protocol is perceived as being relatively constraining, lengthy, and painstaking both by the wearer and by the optician.